This invention relates to a push-pull tool for setting multi-piece fasteners. The invention may be viewed as an improvement or variation of the tools shown in U.S. Pat. No. 4,580,435 issued to G. L. Port et al, and U.S. Pat. No. 4,597,263 issued to Robert Corbett.
U.S. Pat. No. 4,580,435 shows a push-pull tool wherein a piston 20 is moved in one direction by air pressure applied to the right face of the piston. The piston is moved in the opposite direction by hydraulic pressure applied to the left face of the piston. In one specific instance the air pressure was 90 p.s.i., whereas the hydraulic pressure was 3800 p.s.i. (see column 3, lines 17 and 18). While the hydraulic pressure is being applied to the left face of the piston the chamber space to the right of the piston is vented to atmosphere through a clearance opening at trigger 136.
One problem with the tool shown in U.S. Pat. No. 4,580,435 is the fact that over time the high pressure hydraulic fluid tends to be drawn past the piston seals 30 and 32 into the air chamber at the right of the piston. This oil migration can cause the tool to malfunction in extreme cases. Another problem with the patented tool is a low operating pressure on the air side of the piston.
U.S. Pat. No. 4,597,263 shows a push-pull tool wherein hydraulic fluids on opposite faces of piston 74 are alternately pressurized to move the piston to the left and then to the right. The hydraulic system is provided with a pressure relief valve 64 to vent pressurized liquid to the atmosphere in response to pressure surges occurring in the system. Repeated opening of valve 64 can deplete the liquid in the system, thereby degrading the tool performance.